Abstract: In this paper, the AVR single chip is used as the controller of the brushless DC motor-driven system, and realizing the functions of bi-direetional rotation and velocity modulation control through changing the control word transmission order and modulating the duty-ratio of PWM wave. The control circuit of brushless direct current motor mainly focuses on the design for the main circuit, driven circuit and the position signal detecting circuit , and gives the corresponding hardware circuit and the flow chart of software.